Methods for the fractionation and analysis of proteins are developed and applied to the purification of specific proteins for the study of their function and structure. Displacement chromatography is being developed for the fractionation of macromolecules and particles of biological interest, employing polyanions differing in number of charges per molecule as displacers. Recent efforts have been directed toward the fractionation of nonhistone proteins of calf thymus nuclei and marker proteins in human serum. The procedure is particularly advantageous when large amounts of source material must be used to obtain sufficient amounts of a minor component, since the resolving power of the system can be focused on the narrow range of affinity represented by the protein of interest and its nearest neighbors. Recent tests have shown that the system is capable of separating genetic variants that differ in isoelectric point by 0.1 pH unit.